diff -r 000000000000 -r 6474c204b198 browser/base/content/test/newtab/browser_newtab_perwindow_private_browsing.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/browser/base/content/test/newtab/browser_newtab_perwindow_private_browsing.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,68 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+/*
+ * These tests ensure that all changes made to the new tab page in private
+ * browsing mode are discarded after switching back to normal mode again.
+ * The private browsing mode should start with the current grid shown in normal
+ * mode.
+ */
+
+function runTests() {
+  // prepare the grid
+  yield testOnWindow(undefined);
+  yield setLinks("0,1,2,3,4,5,6,7,8,9");
+
+  yield addNewTabPageTab();
+  pinCell(0);
+  checkGrid("0p,1,2,3,4,5,6,7,8");
+
+  // open private window
+  yield testOnWindow({private: true});
+
+  yield addNewTabPageTab();
+  checkGrid("0p,1,2,3,4,5,6,7,8");
+
+  // modify the grid while we're in pb mode
+  yield blockCell(1);
+  checkGrid("0p,2,3,4,5,6,7,8");
+
+  yield unpinCell(0);
+  checkGrid("0,2,3,4,5,6,7,8");
+
+  // open normal window
+  yield testOnWindow(undefined);
+
+  // check that the grid is the same as before entering pb mode
+  yield addNewTabPageTab();
+  checkGrid("0,2,3,4,5,6,7,8")
+}
+
+var windowsToClose = [];
+function testOnWindow(options) {
+  var win = OpenBrowserWindow(options);
+  win.addEventListener("load", function onLoad() {
+    win.removeEventListener("load", onLoad, false);
+    windowsToClose.push(win);
+    gWindow = win;
+    whenDelayedStartupFinished(win, TestRunner.next);
+  }, false);
+}
+
+function whenDelayedStartupFinished(win, callback) {
+  const topic = "browser-delayed-startup-finished";
+  Services.obs.addObserver(function onStartup(subject) {
+    if (win == subject) {
+      Services.obs.removeObserver(onStartup, topic);
+      executeSoon(callback);
+    }
+  }, topic, false);
+}
+
+registerCleanupFunction(function () {
+  gWindow = window;
+  windowsToClose.forEach(function(win) {
+    win.close();
+  });
+});
+